Gas Phase and Surface Modeling of Chemical Vapor Deposition of Pyrolytic Carbon on Silicon Carbide Fibers Using a Pure Methane Precursor PDF Download
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Author: Rajesh Balachandran
Publisher:
ISBN:
Category : Chemical engineering
Languages : en
Pages : 115
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Book Description
Ceramic matrix composites (CMC) constitute a category of composite materials widely used in the aerospace industry as they satisfy the thermal, chemical and mechanical requirements of a good composite material with the drawback being in the high processing costs. Chemical vapor deposition is a process long known for its importance in aerospace and structural applications. Chemical vapor deposition can be used to develop thin interfacial coatings on fibers, which are reinforced in to a matrix according to the application. The interfacial layers are useful for preventing reactions between the fibers and the matrix material at high temperatures. Interfacial coatings can also deflect crack propagation once the composite is put into service. This work focuses on developing a suitable gas phase and surface kinetics model for obtaining the deposition profiles in the chemical vapor deposition of pyrocarbon on silicon carbide fibers at the given conditions of temperature, pressure and feed rate. The model uses an existing gas phase mechanism (National Institute for Standards and Technology and Gas Research Institute). There are combinations of species in the gas phase, but all of them do not lead to the deposition of pyrocarbon. This raises a question as to which of them would affect the rate of deposition and why. For the given conditions of temperature, pressure and flow rate and from the information available in different literature sources acetylene is assumed to be the major depositing specie of pyrocarbon Also, the gas phase mechanism was modified to simplify and suit the needs of the given conditions. The importance behind modeling the surface kinetics is that it could help understand the actual process in the formation of pyrolytic carbon. The mechanism of the pyrocarbon deposition could be important in knowing the type of carbon being deposited, which is of utmost importance in its applications. The modeling data is validated by means of using data obtained from experiments.
Author: Rajesh Balachandran
Publisher:
ISBN:
Category : Chemical engineering
Languages : en
Pages : 115
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Book Description
Ceramic matrix composites (CMC) constitute a category of composite materials widely used in the aerospace industry as they satisfy the thermal, chemical and mechanical requirements of a good composite material with the drawback being in the high processing costs. Chemical vapor deposition is a process long known for its importance in aerospace and structural applications. Chemical vapor deposition can be used to develop thin interfacial coatings on fibers, which are reinforced in to a matrix according to the application. The interfacial layers are useful for preventing reactions between the fibers and the matrix material at high temperatures. Interfacial coatings can also deflect crack propagation once the composite is put into service. This work focuses on developing a suitable gas phase and surface kinetics model for obtaining the deposition profiles in the chemical vapor deposition of pyrocarbon on silicon carbide fibers at the given conditions of temperature, pressure and feed rate. The model uses an existing gas phase mechanism (National Institute for Standards and Technology and Gas Research Institute). There are combinations of species in the gas phase, but all of them do not lead to the deposition of pyrocarbon. This raises a question as to which of them would affect the rate of deposition and why. For the given conditions of temperature, pressure and flow rate and from the information available in different literature sources acetylene is assumed to be the major depositing specie of pyrocarbon Also, the gas phase mechanism was modified to simplify and suit the needs of the given conditions. The importance behind modeling the surface kinetics is that it could help understand the actual process in the formation of pyrolytic carbon. The mechanism of the pyrocarbon deposition could be important in knowing the type of carbon being deposited, which is of utmost importance in its applications. The modeling data is validated by means of using data obtained from experiments.
Author: Mia Catherine Matt
Publisher:
ISBN:
Category :
Languages : en
Pages : 168
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Book Description
Laser chemical vapor deposition (LCVD) is a processing technique that can be used to grow fibers. In this study, the relationships between deposited SiC fiber composition, fiber microstructure, and fiber mechanical properties (ambient temperature failure stress in tension) were compared using two different precursor gases - Tetramethylsilane (TMS) and Dimethylsilane (DMS) 0́3 using laser chemical vapor deposition (LCVD). Each set of fibers was grown at 2, 4 and 6 bar at a growth rate of 50 um/s. Furthermore, each set of fibers contained a nanocrystalline core. In some cases, the presence of nodular structures were noted, but these features were comprised of nanocrystalline grains. The crystalline structure for both fibers were indexed by X-ray diffraction as the 3C-SiC cubic phase. The fibers were carbon-rich. In general, the TMS fibers had generally higher average stress at failures that were 2280 MPa as compared to the average DMS fibers being 1150 MPa. Considerable spread in the tensile strength at failure was noted for the DMS fibers and is contributed to residual stresses, as they fibers were qualitatively more delicate to handle. A Weibull analysis revealed that the fibers had a low Weibull modulus, which is an indication of a large and unpredictable variation of flaws within the fibers.
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 944
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Author: Suleyman Akif Gokoglu
Publisher:
ISBN:
Category : Chemical kinetics
Languages : en
Pages : 14
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Author: Joseph P. Copeland
Publisher:
ISBN:
Category :
Languages : en
Pages : 153
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Book Description
Codeposited coatings of pyrolytic graphite/silicon carbide were fabricated by chemical vapor deposition at temperatures ranging from 3000 F to 3800 F using methane and methyltrichlorosilane as precursors and nitrogen as a diluent and carrier. The effect of temperature and methyltrichlorosilane concentration on coating composition (SiC content) and morphology were determined. Specimens of codeposited coatings were fabricated to determine the physical properties, thermal stress state and erosion characteristics of various PG/SiC compositions. Coating samples were examined and characterized microscopically, by X-ray diffraction and by electron microprobe. (Author).
Author: T. C. Wallace
Publisher:
ISBN:
Category :
Languages : en
Pages : 201
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Book Description
A series of instrumented engineering tests is described in which a 'channel flow' chemical vapor deposition furnace was used to prepare pyrolytic graphite/silicon carbide (PG/SiC) codeposited material for rocket-nozzle applications. The nozzle section and a water cooled center body formed a vertical annular flow passage for the coating gases. The nozzle section was inductively heated and was coated on the i.d. only. Well-mixed process gas entered the flow annulus with uniform velocity, temperature, and species concentrations from a plenum below the heated substrate. The flow could be either laminar or turbulent, but did not contain recirculating regions. An analytical model of the furnace and deposition process was developed to simulate the heat transfer in the solid components and the flow, chemical kinetics, and heat and mass transport associated with the process gas. Model predictions and test results on temperatures and PG/SiC deposition rates agreed very well. The coating microstructure and inferred quality were characterized by metallography and correlated with the process variables. The report includes detailed descriptions of the furnace, instrumentation, and test procedures in addition to plots of all reduced data. (Author).
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 43
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Book Description
Deposition of pyrolytic carbon on the surface of carbon substrates, including carbon fibers, was studied at 1000-1100 C using two different systems, a static reactor operating at subambient pressures and a flow reactor operating at atmospheric pressure. The experimental parameters that affect the deposition rates and mechanism are substrate temperature, type of reactor used, total and partial pressure of methane in the static reactor, partial pressure of methane in the flow reactor, flow rate of hydrocarbon above substrate, presence of hydrogen in the deposition medium, and the type of substrate, as well as its surface area. The two main differences between the deposition under flow and static conditions are rates of deposition and characteristics of deposits. While the rate under flow conditions is considerably higher than under static conditions, the deposits in the flow reactor are intact and less porous than those prepared in the static reactor. This is attributed essentially to the presence of hydrogen in the static reactor which lowers the rates of deposition, prevents the growth of intermediate species to large planar molecules, and attacks the carbon deposits.
Author: Andrew Y. C. Nee
Publisher: Springer
ISBN: 9781447146698
Category : Technology & Engineering
Languages : en
Pages : 0
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Book Description
The Springer Reference Work Handbook of Manufacturing Engineering and Technology provides overviews and in-depth and authoritative analyses on the basic and cutting-edge manufacturing technologies and sciences across a broad spectrum of areas. These topics are commonly encountered in industries as well as in academia. Manufacturing engineering curricula across universities are now essential topics covered in major universities worldwide.
Author: T. C. Wallace
Publisher:
ISBN:
Category :
Languages : en
Pages : 213
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Book Description
A series of instrumented engineering tests with a chemical vapor deposition furnace used to prepare pyrographite/silicon carbide codeposited material for rocket nozzle applications is described. Flow into the furnace is an axisymmetric confined jet with high Reynolds and low Mach number. The gas flow within the furnace is characterized by a large separated flow region with associated hot spot and a high level of turbulence. Methods of instrumenting and collecting data, methods for defining the furnace and process characteristics, test procedures, recording and reducing data, data analysis, and model development are documented. Analytical models of the furnace during transient and steady state operation were developed and the results compared with the data obtained. Characterization of the coatings obtained and the associated deposition kinetics are also presented. (Author).
Author:
Publisher:
ISBN:
Category : Chemistry
Languages : en
Pages : 2616
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